Typically, in commercial photomultiplier tube-based positron emission tomography systems, a potentiometer is adjusted so that each photomultiplier tube signal amplitude is identical within the scanner or at least for each block detector. A scintillator array or light pulser is optically coupled to the photomultiplier tubes and the light pulses are used to adjust each photomultiplier tube in a positron emission tomography system. This is not very exact since the light pulses may not have the same exact light output; therefore, the gain adjustment is based on an average of light pulse outputs. This procedure is usually done by hand, by a trained technician, using a voltage potentiometer attached to the voltage circuit.
Desirable in the art is an improved photosensor and a calibration system that would improve upon the conventional PET systems.